1. Technical Field
The invention relates generally to optical scanning, such as near-field scanning optical microscopy.
2. Description of Related Art
Scanning Probe Microscopy has enabled imaging of surfaces at the nanometer scale by employing a fine probe that is scanned over a surface (or the surface is scanned under the probe), rendering resolutions that are no longer constrained by the wavelength of light or electrons and that can resolve individual atoms. Different actual techniques have been developed under the general guise of Scanning Probe Microscopy, including STM (scanning tunneling microscopy), AFM (atomic force microscopy), and NSOM (Near-Field Scanning Optical Microscopy).
NSOM typically uses laser light emitted through an aperture much smaller than the wavelength of the light (on the order of less than 100 nm), thus achieving resolutions better than the diffraction limit. The probe, however, must be scanned much closer to the surface than the wavelength of the light. Typically, the laser light is fed to the aperture through an optical fiber and the aperture itself is the sharpened or tapered end of the fiber, which can also be coated with a metal such as Al. Different types of feedback mechanisms can be employed to maintain the required probe-to-surface distance, but the most common are by using a cantilevered probe to monitor the normal force through beam-deflection, and by using a tuning fork attached to the fiber and oscillating at its resonant frequency to monitor changes in the vibration amplitude as the probe moves over the surface (also known as “shear-force” feedback).
Examples of optical near-field scanning microscopes are known, and include near field scanning microscopes having a tapered waveguide, fiber optic probes, high resolution fiber optic probes for near field scanning, near-field scanning optical microscope probes exhibiting resonant plasmon excitation, as well as methods and devices for near-field scanning optical microscopy by reflective optical feedback.
An NSOM may be operated in a number of modes, typically selected in view of the sample to be imaged. In transmission mode, the light travels through the probe aperture and is transmitted through the sample (and therefore requires a transparent sample). In reflection mode, the light travels through the probe aperture and is reflected by the surface. In collection mode, the sample is illuminated by a large outside light source and the probe collects the reflected light. And in illumination/collection mode, the probe both illuminates the sample and collects the reflected light.
As can be appreciated, most modes of operation can stand to benefit from a probe that can emitter a brighter (stronger) light. The present writing addresses this need.